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Abstract:

Advanced oxidation processes (AOPs) are being developed to enhance the disinfection efficacy of indicator organisms in situations where a single disinfecting agent, such as ultraviolet radiation (UV), is less effective, e.g. as in case of effluents with low UV-transmissivity (UVT).
Bench scale study used peracetic acid (PAA) and UV, either combined (referred to as AOP) or individually, to inactivate fecal coliform bacteria (FC) from biological effluent collected during dry weather flow conditions. Treatments tested consist of various combinations of PAA (0, 2, and 8
mg/L) and/or UV radiation (0, 5, 10, 20, and 40mWs/cm2). In combination runs PAA solution was added prior to UV irradiation. A low-pressure collimated beam apparatus was used to irradiate the 50 mL samples in a crystallization dish. Results indicated that treatments with PAA alone
were inadequate for reduction of FC to the standard discharge limit (200-MPN/100 mL) within the contact time given (<10 min). Individual and combined UV treatments were found to effectively inactivate the FC. The UV treatment alone required 28 mWs/cm2 fluence, whereas the addition
of 2 mg PAA/L required 22-mWs/cm2 - resulting in a 21% saving in UV energy. The 8 mg PAA/L with 10mWs/cm2 UV combination out-performed all the treatment methods. It produced the required effluent quality with 64% reduction in power required. It was determined that the
rapid inactivation of fecal coliform bacteria from AOP treatments was attributed to a synergistic effect of the two disinfecting agents. The results confirm technical applicability of this AOP method to disinfection of biological wastewater effluents. The use of PAA in combination with UV
may be hindered by the need to provide long contact time for the chemical to be effective.

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